In general, polyurethane foams have been employed as an insulator between an inner box and an outer case of a refrigerator; and CFC(chlorofluorocarbon) has been employed as a foaming agent in manufacturing the polyurethane forms. However, the use of CFC has become restricted since CFC was found to destroy the ozone layer in the stratosphere.
Accordingly, CFC is being replaced with HCFC which is known to be less destructive of the ozone layer. However, when HCFC is employed as the foaming agent, it tends to cause severe environmental stress in the ABS(acrylonitrile-butadiene-styrene) resin which is used in building the inner box of a refrigerator, rendering the ABS resin unsuitable for use in the manufacture of a refrigerator cabinet. Accordingly, an alternative resin having suitable HCFC resistance has been sought to replace the ABS resin.
In this connection, it has been known that the more nitrile is added to a resin, the higher resistance to chemicals in general is obtained(see U.S. Pat. No. 3,426,102). However, if the content of nitrile in a resin is too high, the impact strength and the fluidity of the resin are deteriorated and, furthermore, the color thereof tends to change to yellow.
Consequently, needs have continued to exist for the development of a resin which is resistant to HCFC without the above and other deficiencies.